Polyacetal resin has an excellent balance among mechanical strength, chemical resistance, sliding properties and abrasion resistance, and also, it is easily processed. Accordingly, polyacetal resin has been used as a typical engineering plastic in a broad range including mechanism elements of electric equipment, automobile components, and other mechanism elements.
When the polyacetal resin is selected for these intended uses, the most important thing is good sliding properties of the polyacetal resin. For example, in the case of a printer gear or a window motor gear for cars, rubbing against (friction with) other materials takes place under conditions of relatively high load (approximately 10 to 20 N of load). At that time, it is important for the polyacetal resin to have high sliding properties by which it is not abraded, or quietness by which it causes a little rubbing noise or creaking noise.
For the purpose of improving abrasion resistance or quietness under such a high load, for example, Patent Literature 1 proposes a technique of adding an ester compound as a sliding agent to the polyacetal resin, and Patent Literature 2 proposes a technique of adding polyolefin as a sliding agent to the polyacetal resin. Further, Patent Literature 3 proposes a technique of adding an elastomer and a sliding agent to the polyacetal resin, and the like.
On the other hand, for example, as described in Patent Literature 4, the polyacetal resin has been recently used in a component called “lamp” in hard disk drive.
This component called lamp is a component used for a slider head serving as a reading/writing part to evacuate from the hard disk, when reading/writing into the hard disk is in a non-working state.
When the slider head goes in and out the lamp, the tab on the edge of the head rubs against the inclined portion of the lamp. The load during the rubbing is very small (a load of approximately 0.05 N or less).
There are many cases where the aforementioned material having high sliding properties under a high load (a load of approximately 10 to 20 N) cannot be directly applied as a material under a very small load (a load of 0.05 N or less), nor vice versa. For instance, when a material that has excellent sliding properties in a gear is applied to a lamp component, it does not always provide a component having good performance.
From such a viewpoint, materials have been developed so far for use in hard disk lamp components. For example, Patent Literatures 5 and 6 each propose a resin composition prepared by adding a polymer lubricant having a weight average molecular weight of more than 10,000, such as polyolefin, to the polyacetal resin as a suitable material for hard disk lamp components.